Seismic prospecting

ABSTRACT

A method of seismic prospecting wherein detonating cord is laid parallel to the surface of a prospect area, a quantity of a fluent explosive, for example a free-running powdered or slurried blasting explosive, is placed adjacent to the cord, and the cord and explosive are detonated.

0 United States P316111 1111 3,729,6 Murray 5] Apr. 21, 19 73 15 SEISMIC PROSPECTING 3,523,425 8/1970 Pierce, Jr. Inventor: Frank McDonald y, Kflmap 1,006,116 10/1911 Morse ..6l/72.6

Scotland FOREIGN PATENTS OR APPLICATIONS [731 Assignee Imperial Chemical Industries 815,295 6/1969 Canada ..1s1/0.5 xc

Limited, London, England 221 Filed: July 27, 1970 OTHER PUBLICATIONS The Davis C0n\/el Charge, Davis Equip. C0., Nov., [2] 1 Appl' 58580 1961, Broomstick Distributed Charge.

[30] Foreign Application Priority Data Primary Examiner--H. A. Borchelt Aug. 13, 1969 Great Britain ..40,4l4/69 Amman Examiner' Bmmel Attorney-Cushman, Darby & Cushman [52] US. Cl. ..l81/0.5 XC, 6l/72.6, 6l/72.2 I 51 Int. Cl. ..G01v 1/13, E02f 5/10 [57] ABSTRACT [58] Field of Search ..l8l/O.5 XC; 61/726, A h d f i i prospecting wherein detonating 61/722 cord is laid parallel to the surface of a prospect area, a H quantity of a fluent explosive, for example a free- 1 References C'ted running powdered or slurried blasting explosive, is

' UNITED STATES PATENTS placed adjacent to the cord, and the cord and exploslve are detonated. 3,456,450 7/1969 Teichmann ..l81/O.5 XC 3,354,660 11/1967 Vaughan ..61/72.2 11 Claims, 1 Drawing Figure Pqtexited April 24, 1913 3,729,065

v p? 4/0%M SEISMIC PROSPECTING invention relates to a method of seismic prospecting and to an apparatus for placing explosive charges in position in the said method.

In land and marine seismic prospecting it is usual to detonate explosive charges at the prospect area and to record the seismic waves reflected or refracted from subterranean rock layer interfaces. In a recently developed method described in U.K. Patent Specifications Nos. 1,151,882 and 1,151,883, a flexible elongated explosive charge, for example detonating cord, is placed under stemming parallel to the surface of a prospect area. The seismic signal can be improved if auxiliary charges of explosive are connected to the elongated explosive charge so as to be exploded by the transmission of the detonation wave therefrom.

We have now found that it is advantageous to place in detonation transmission relation to the elongated explosive an auxiliary charge of a fluent explosive material which is capable of being initiated by the explosion of the elongated explosive, the fluent material being either continuous or in slugs. We have also devised an apparatus for simultaneously placing the elongated explosive and the fluent explosive in position for firing for seismic prospecting.

In accordance with this invention a method of seismic prospecting comprises laying a line of elongated explosive adjacent to and substantially parallel to the surface of a prospect area, placing fluent explosive material in detonation transmission relation to said line and detonating said line.

The fluent explosive material may be disposed continuously or at intervals along the elongated explosive. Preferably the line of elongated explosive and the fluent explosive are covered by stemming material and stemming is advantageously effected by sinking the elongated explosive and the fluent material below the surface of the prospect area. In the preferred method, in which detonating cord is used as the elongated explosive, a line of detonating cord and the fluent explosive material are sunk below a land or water surface by simultaneously passing them down through the same conduit or separate conduits extending into the surface layer and moved parallel thereto. ln land seismic prospecting the conduit or conduits may advantageously be attached to a plough member adapted to penetrate the upper ground layer of a prospect area to displace earth and form a temporary opening therein to receive the detonating cord and the fluent explosive material as the plough member is moved parallel to the ground surface, the displaced earth closing around the cord and fluent explosive material as they emerge from the lower end of the conduit.

The fluent explosive material is preferably a powder, thickened liquid or a slurried explosive composition. Especially useful compositions are the sensitised ammoniu m nitrate powder or slurry explosives, the preferred compositions being those which are sufficiently sensitive for initiation by detonating cord. For example, a granular TNT/ammonium nitrate composition or a composition of the AN/FO type containing (by weight) 1 to 4 parts of fuel oil to 99 to 96 parts of ammonium nitrate and optionally O to parts of aluminium may be advantageously used; Likewise, a slurried explosive composition comprising ammonium nitrate, water, a thickening agent for the water, fuel and a sensitiser, for example PETN or isopropyl nitrate, is also advantageous.

The apparatus of the invention comprises tubular conduit means through which a line of elongated explosive may be fed in a continuous manner, into a position on or in the upper surface layer of a prospect area, and substantially parallel to the surface thereof, as the conduit means is moved over the prospect area, and through which conduit means a fluent explosive may also be fed in continuous or intermittent manner into detonation transmission relation with said elongated explosive, means to move the conduit over the prospect area and means to control the rate of flow or" fluent explosive material through the conduit means.

The conduit means may comprise a single tubular conduit through which both the elongated explosive and the fluent explosive material are fed but preferably there are individual tubular conduits for the respective explosives. An advantageous arrangement comprises two tubes, one inside the other, the inner tube providing a passage for the line of elongated explosive and a space between the tubes providing a passage for the fluent explosive material. Preferably the conduit means are fabricated from non-ferrous material, for example copper, brass, aluminium or synthetic plastics. The flow control means for the fluent material advantageously comprises gate means arranged to obturate the tubular conduit through which the fluent explosive material is fed. When the fluent material is to be pumped rather than fed under gravity, the flow may be controlled by means ofa metering pump.

In a preferred apparatus suitable for burying the explosive charges the conduit means is attached to a plough member adapted to penetrate and to be moved through the upper ground layer of a prospect area as the apparatus is moved parallel to the ground surface whereby a temporary opening is formed in said layer into which opening the elongated explosive and the fluent explosive are fed. In this form of the apparatus the frictional pull of the earth closing around the elongated explosive is usually sufficient to pull the elongated explosive through the conduit thereby obviating the need for positive feed means for this explosive. If desired, the end of a detonating cord may be positively anchored in position. The plough member conveniently comprises a rigid elongated member adapted to penetrate the ground in a generally upright manner. In order to urge the plough member downwards, the lower end of the plough member is preferably formed with a forward and downward inclined leading face and may advantageously be provided as a shoe attached to an upright plough member. In operation the apparatus, together with storage means for supplies of elongated explosive and fluent explosive material, is conveniently mounted on a vehicle for towing.

In order to further illustrate the invention a preferred apparatus is hereinafter described, by way of example only, with reference to the accompanying drawing which shows diagrammatically, in sectional elevation,

the apparatus in use for burying a line of detonating cord and a fluent explosive charge. Although the drawing shows only one detonating cord and auxiliary charges of fluent explosive material, it will be understood that two or more parallel lines of detonating cord together with associated auxiliary charges may be placed simultaneously.

As shown in the drawing, a towed plough member mounted on a towed frame member 11, adapted for towing by a tractor (not shown), penetrates the upper ground layer 12 ofa prospect area to form a temporary opening therein. A tubular conduit 13 has a hopper 14 mounted on top and has an inner conduit 15 mounted within. The conduit 13 extends almost to the lower end of the plough member 10 and terminates in a downward facing aperture 16. The conduit 15 extends from the top of the hopper l4 and emerges at the aperture 16. The lower end of the conduit 15 has an endpiece 17 attached by a flexible jointing tube 18 which permits free vertical and horizontal movement of the end-piece and thereby avoids damage ofthe detonating cord.

Detonating cord 19 is led from a supply reel 20 mounted on a frame member 11 over a guide roller 21 through conduit 15 downwards into the ground where it is gripped by the earth which closes around it. A supply of fluent explosive material 22 is stored in hopper 14 and fed through conduit 13 and aperture 16 into the temporary opening formed in the ground layer 12 where it is disposed around the detonating cord 19. The feed of fluent explosive material is controlled as desired by a gate 23 which adjustably obturates the conduit 13.

As illustrated, the fluent explosive material is a slurry explosive which is being fed in slugs. The explosive could equally well be fed continuously and it could, if desired, be any other fluent explosive material.

When the detonating cord and fluent explosive material are buried in the manner illustrated and the cord is detonated, the auxiliary fluent explosive also detonates. The energy of the seismic wave generated may thus be increased markedly beyond that obtainable from detonating cord alone. 7

For putting the invention into practice Geoflex (Registered Trade Mark) detonating cord comprising a core of pentaerythritol tetranitrate within a waterproof sheath is convenient.

What we claim is:

l. A method of seismic prospecting which comprises laying a line of elongated explosive adjacent to and substantially parallel to the surface of a prospect area, simultaneously pouring fluent explosive material around the line of elongated explosive as the line is placed in position and detontaing said line.

2. A method as claimed in claim 1 wherein the elongated explosive and the fluent explosive are sunk below the surface ofa prospect area.

3. A method as claimed in claim 1 wherein a line of detonating cord and the fluent explosive material are sunk below a land or water surface by simultaneously passing them down through the same conduit or separate conduits extending into the surface layer and moved parallel thereto.

4. A method of land seismic prospecting as claimed in claim 3 wherein the conduit or conduits are attached to a plough member adapted to penetrate the upper ground layer of a prospect area to displace earth and form a temporary opening therein to receive the detonating cord and the fluent explosive material as the plough member is moved parallel to the ground surface, the displaced earth closing around the cord and fluent explosive material as they emerge from the lower end of the conduit.

5. A method as claimed in claim 1 wherein the fluent explosive material comprises an explosive selected from the group consisting ofa powder, thickened liquid or a slurried explosive composition.

6. A method as claimed in claim 5 wherein the fluent explosive material comprises an explosive selected from the group consisting of a granular TNT/ammonium nitrate composition, an AN/FO explosive composition and an ammonium nitrate slurried explosive containing asensitiser selected from the group consisting of PETN and isopropyl nitrate.

7. Apparatus for placing explosive charges in position for seismic prospecting comprising: support means adapted to be advanced over a prospect area, tubular conduit means carried by the support means for continuously feeding a line of elongated explosive into a position on or in the upper surface layer of the prospect area and substantially parallel to the surface thereof and for simultaneously passing a fluent explosive into contact with the elongated explosive, and means for forming the fluent explosive passing through said eonduit means into spaced-apart slugs, said means comprising valve means for intermittently stopping the flow of fluent explosive through said conduit means.

8. An apparatus as claimed in claim 7 wherein the conduit means comprises two tubes, one inside the other, the inner tube providing a passage for the line of elongated explosive and a space between the tubes providing a passage for the fluent explosive material.

9. An apparatus as claimed in claim 8 wherein the conduit means is fabricated from a material selected from the group consisting of copper, brass, aluminium or synthetic plastics.

10. Apparatus as in claim 7 wherein said valve means includes a gate valve.

11. An apparatus as claimed in claim 7 wherein the conduit means is attached to a plough member adapted to penetrate and to be moved through the upper ground layer of a prospect area as the apparatus is moved parallel to the ground surface, whereby a temporary opening is formed in said layer into which open ing the elongated explosive and the fluent explosive are fed. 

1. A method of seismic prospecting which comprises laying a line of elongated explosive adjacent to and substantially parallel to the surface of a prospect area, simultaneously pouring fluent explosive material around the line of elongated explosive as the line is placed in position and detontaing said line.
 2. A method as claimed in claim 1 wherein the elongated explosive and the fluent explosive are sunk below the surface of a prospect area.
 3. A method as claimed in claim 1 wherein a line of detonating cord and the fluent explosive material are sunk below a land or water surface by simultaneously passing them down through the same conduit or separate conduits extending into the surface layer and moved parallel thereto.
 4. A method of land seismic prospecting as claimed in claim 3 wherein the conduit or conduits are attached to a plough member adapted to penetrate the upper ground layer of a prospect area to displace earth and form a temporary opening therein to receive the detonating cord and the fluent explosive material as the plough member is moved parallel to the ground surface, the displaced earth closing around the cord and fluent explosive material as they emerge from the lower end of the conduit.
 5. A method as claimed in claim 1 wherein the fluent explosive material comprises an explosive selected from the group consisting of a powder, thickened liquid or a slurried explosive composition.
 6. A method as claimed in claim 5 wherein the fluent explosive material comprises an explosive selected from the group consisting of a granular TNT/ammonium nitrate composition, an AN/FO explosive composition and an ammonium nitrate slurried explosive containing a sensitiser selected from the group consisting of PETN and isopropyl nitrate.
 7. Apparatus for placing explosive charges in position for seismic prospecting comprising: support means adapted to be advanced over a prospect area, tubular conduit means carried by the support means for continuously feeding a line of elongated explosive into a position on or in the upper surface layer of the prospect area and substantially parallel to tHe surface thereof and for simultaneously passing a fluent explosive into contact with the elongated explosive, and means for forming the fluent explosive passing through said conduit means into spaced-apart slugs, said means comprising valve means for intermittently stopping the flow of fluent explosive through said conduit means.
 8. An apparatus as claimed in claim 7 wherein the conduit means comprises two tubes, one inside the other, the inner tube providing a passage for the line of elongated explosive and a space between the tubes providing a passage for the fluent explosive material.
 9. An apparatus as claimed in claim 8 wherein the conduit means is fabricated from a material selected from the group consisting of copper, brass, aluminium or synthetic plastics.
 10. Apparatus as in claim 7 wherein said valve means includes a gate valve.
 11. An apparatus as claimed in claim 7 wherein the conduit means is attached to a plough member adapted to penetrate and to be moved through the upper ground layer of a prospect area as the apparatus is moved parallel to the ground surface, whereby a temporary opening is formed in said layer into which opening the elongated explosive and the fluent explosive are fed. 